The invention relates to a conveyor chain for machines for tensioning lengths of material according to the preamable to claim 1.
Lengths or webs of plastic and textile material are principally passed through tensioning machines whilst being guided widthways for the purpose of processing (e.g. drying and/or fixing and cooling), during which these transport chains grip the lengths of material to be processed on their long edges by means of grippers or needle plates. Depending upon the type of material and the processing to which it is to be subjected it is generally known in the art to use two different types of conveyor chain, namely on the one hand so-called sliding chains which are preferably used at high material speeds and high temperatures (with only limited requirements for maintenance and lubrication) and on the other hand so-called rolling chains which are preferred for particularly high transverse tensional forces in the lengths of material (e.g. in industrial fabrics or the like) and at their joints have ball bearings on the outer races of which they are supported so as to be able to roll on longitudinal guide rails of a chain guide and as a result can take up high transverse tensional forces very well. The present invention relates to the last-mentioned construction.
Conveyor chains of the last-mentioned construction are sufficiently known in the art. Whilst in these the ball bearings are mounted on the outer peripheral surface of the joint sleeves, the inner peripheral surfaces of these joint sleeves can be articulated on the appertaining chain joint bolts by means of sliding bearing sleeves. Sliding bearing sleeves inside the joint sleeves together with the chain joint bolts form the actual chain joints. Whilst the ball bearings mounted on the outer peripheral surfaces of the joint sleeves serve both for the rolling support (to accommodate high transverse tensional forces in the length of material) and also for the chain turn-round. In practice these conveyor chains in the form of rolling chains have proved to have some shortcomings: For reasons of cost the conveyor chains which are used should be produced with normal manufacturing precision. As a result the chain joint bolts generally deviate from their desired normal position by a few minutes of a degree, resulting in an undesirable end pressure in the sliding bearing sleeves of these chain joints which leads to premature wear. In addition, the ball bearings which are usually used have outer races which have a relatively high elasticity. The transverse tensional forces of lengths of material to be processed lead to punctiform loads on the outer races of the ball bearings, as a result of which during operation they are slightly deformed upon introduction of force to an approximately oval shape, which is also undesirable.
These disadvantages of the known construction can only be avoided in part by another equally known conveyor chain in which needle bearings can be used in place of sliding bearing sleeves.